MICROCAPILLARY ELECTRODES FOR INTRACELLULAR RECORDING 



engages a gravity arm. This arm is lifted over the teeth and also actuates 

 a switch which cuts oflF power to the solenoid. 



This apparatus is discussed in some detail as it is one to be recommended 

 for the reliable production of a variety of microelectrodes. 



Fine microelectrodes are usually made of Pyrex or Phoenix glass, the 

 latter having a slightly lower softening point. For constant results tubing 

 of fixed size and proportion should be used. The glass recommended by 

 Alexander and Nastuk^^ is 2 mm outside diameter and 1-3 mm internal 

 diameter; but glass from 1-2-3 mm has been used. Glass of constant size 

 can be ordered from manufacturers or hand-produced, cut into constant 

 lengths of about 4 cm and selected to specified hmits with a micrometer. 



Examination and testing — The initial setting up of an electrode puller 

 can be laborious, and systematic exploration is advisable. Electrodes 

 drawn are first examined with a low power microscope when gross features 

 are determined. The actual tip itself is often difficult to see clearly because 

 of interference fringes which, at times, produce an apparently undulating 

 surface or sharp taper. 



It is advisable to fill electrodes as soon as possible. They are re-examined 

 when full, with a water immersion objective, usually 1/6 in., when the image 

 of the tip is clearer and the artefacts seen earlier are not apparent. The 

 resistance of the electrodes is then determined, but whether the electrodes 

 are in fact effective can only be decided by direct experiment. 



Methods of filling capillary electrodes with electrolytes 



It is advisable to fill electrodes with fluid soon after they are formed, as 

 dust and moisture tend to adhere to them and even enter the lumen. 



■To suction pump 



fice for equalizing 

 pressures 



Stem 



=^L. — Rubber band 



— Solution 



Shoulder 



Shank 



-Tip 



(a) (b) 



Figure 35.4 Arrangement for filling and storing microelectrodes 



Electrodes are filled in the vertical position tip downwards. A simple 

 method is shown in Figure 35.4 where the electrodes are secured by an 

 elastic band around the lower end of a glass cylinder held by a rubber 

 stopper in a large flask, which can be evacuated. 



541 



